1. Field of the Invention
The present invention concerns a mechanism for cleaning a driven blanket cylinder of an offset lithographic printing press by means of a wash cloth which is unwound incrementally from a magazine roller, is wetted with a cleaning fluid, is conducted over a pressure mechanism and pressed against the blanket cylinder to be cleaned and is wound up on a take-up roller.
2. Prior Art
In offset lithographic printing presses, the surfaces of the blanket cylinders become contaminated periodically during use. In such an offset lithographic printing press, the driven blanket cylinder generally becomes covered with a variety of different substances some of which are water soluble and some of which are not. To clean such a cylinder effectively, it is necessary that the blanket cylinder be washed with materials which are solvents for each of the contaminants generally found on the surface of the cylinder. Usually, this requires the application of both water and other, nonaqueous solvents to the surface. Furthermore, before the blanket cylinder may be reused, it must be dried of the solvents utilized during its cleaning. Furthermore, for the various solvents which are applied to be fully effective, it is preferable that in at least some instances, the previously applied solvent be essentially removed prior to application of subsequent solvents.
In most offset lithographic printing press operations, it is necessary that the blanket cylinder be cleaned several times a day. To date, no commercially available apparatus can clean the blanket cylinder rapidly and completely so that the offset lithographic printing press is not removed from service for any extended period of time. Although a number of schemes have been sugggested in the prior art, none has been commercially accepted since they are not flexible enough or fast enough to achieve suitable results. As a result, the conventional means of cleaning the blanket cylinders of offset lithographic printing presses remains the manual application and wiping of the cylinder by an operator. Obviously, such a technique is slow and subject to unpredictable results.
Attempts have been made to mechanize this cleaning process. Such a mechanism is shown, for example, in U.S. Pat. No. 2,525,982, to Wescott wherein the wash cloth in the area of the surface to be cleaned on the driven blanket cylinder is pressed thereagainst by a pad. Wescott teaches an apparatus in which a cleaning cloth is manually advanced between a pair of reels. In between the two reels, the cleaning cloth advances over the surface of a generally T-shaped pad which may be pressed against the surface of the blanket cylinder with the wash cloth between the pad and the cylinder. An appropriate cleaning solution is applied to the cloth through the pad by wetting a wick attached to the back of the pad with that desired cleaning solution. The cleaning fluid is then transported to the surface of the pad by capillary action and there wets the cleaning cloth. The cleaning cloth being a highly porous material transports the cleaning solution to the surface of the driven cylinder. During the cleaning of the cylinder, the blanket cylinder rotates relative to the cleaning cloth and a wiping action of the surface is thereby achieved. When the wash cloth becomes soiled, the pad is retracted from the surface of the cylinder and a new section of clean wash cloth is advanced into position over the pad.
While, in principle, this arrangement is advantageous for the cleaning of such cylinders in offset lithographic printing presses, a number of disadvantages occur which prevent the apparatus from performing acceptably. For example, the apparatus is too slow for use in offset lithographic presses where the blanket cylinder is turning at essentially operational speeds. It is necessary to reduce the press speed to the "crawling" mode for cleaning. A definite time lag occurs between the application of the cleaning solution to the wick and the initial arrival of that solution at the surface of the blanket cylinder where it can be utilized. This time lag has a corollary effect which is even more disadvantageous. Once the application of cleaning fluid to the surface of the wick has been discontinued, a considerable period of time elapses before that cleaning solution ceases to arrive at the front surface of the pad over which the cleaning cloth passes. This is similar to an attempt to totally remove a fluid from a sponge. Therefore, the pad cannot be used as part of an apparatus for applying a dry cloth to the surface of the cylinder for that considerable time after the cleaning of that surface. The drying action, which is required, must either be done manually or by some other ancillary apparatus which is neither shown nor suggested in Westcott.
Furthermore, as stated above, it is often necessary when cleaning the surface of such cylinders that more than one cleaning agent be utilized in a sequential program. The examplary agents are water and other, nonaqueous solvents for printing inks. The Wescott apparatus cannot reasonably be utilized for such sequential application of totally different solvent materials. The time lag between the discontinuance of the application of one solvent to the wick and the time necessary to purge the wick of that solvent is such that a single pad, wick and cloth combination can only be utilized practically to apply a single solvent material to the surface of the cylinder or to dry the surface. Therefore, if more than one solvent is necessary for the cleaning of such an offset lithographic press cylinder, more than one of the Wescott apparatus must be supplied for applying that solvent and another apparatus for the drying function.
The pad which is utilized to press the cleaning cloth against the surface of the blanket cylinder in Wescott is also subject to rapid contamination and subsequent inoperability thereby producing an apparatus in which the pad and wick combination must be frequently changed. That is, the wash cloth material necessarily must be highly porous in order to achieve its cleansing function. That porosity allows the contaminated material removed from the surface of the blanket cylinder to be transported back through the cloth and into at least the surface of the pad forcing that cloth against the cylinder. If this material dries and cakes into the pores of the pad, it becomes increasingly difficult for the cleansing solution to advance through the pad to the wash cloth and the blanket cylinder of the offset lithographic printing press thereby requiring either changing or separate cleaning of the wick and pad. Furthermore, once contaminated, the pad can serve as a means for supplying a contaminated cleaning agent to the blanket cylinder thereby degrading the possible end result.
Also, no means are provided in the Wescott apparatus for retaining any degree of tension in the web which is being advanced over the pad. Necessarily, as the web passes, and is wet with the cleaning solution, the web stretches, particularly under the wiping action of the blanket cylinder. As a result, considerable slack necessarily results in the web. Such slack will also tend to contaminate other areas of the apparatus and is, in general, highly undesirable in commercial offset lithographic printing presses.
Another prior art mechanism is shown in West German O. S. No. 2,052,996 to Lawrence. This apparatus utilizes a cleaning web which is pressed against a surface to be cleaned on a drum by a pressure roll. The web is, however, not moistened with a cleaning fluid at any time; the web has a coating on a web of polyurethane, a plain paper or cloth. In other words, any cleaning agent is impregnated into the web at all times. The web is incrementally advanced by pivoting the apparatus vertically by gravity during the time that the pressure roll is traversing the axial space in the surface of the drum. During this time, gravity causes the mechanism including the roll to pivot downwardly. Such action allows the ratchet mechanism shown in FIG. 1 to incrementally advance the web if the rotational speed is sufficiently slow to allow a significant vertical pivoting of the apparatus.
Such rotational speeds are obviously far below the normal operational speeds of modern offset lithographic printing presses. Furthermore, no flexibility is allowable as to type or presence of cleaning agent. The cleaning agent impregnated into the web is always present.
In other areas of the printing industry, it has been known to use wiping webs for removal of excessive deposits of ink and for directing ink into desired areas of a plate and removing ink from other areas. For example, U.S. Pat. No. 282,995 to Lee shows the use of a series of intermittently advanced webs for improved inking of the engraved printing plates of an intaglio printing press. Some of the webs are premoistened and some are not. However, cleaning and removal of inks and other contaminants is not intended or desired. Furthermore, no flexibility exists for a web's condition, i.e., wet or dry. Hence, this apparatus cannot be transferred directly into an offset lithographic printing press, considerable unsuggested modification must first be made.